We have highly purified tetanus toxin by both the cell extract and culture filtrate procedures. The amino acid composition of toxin prepared by both procedures was completed and agrees with that reported by other laboratories. The ordered structure of toxin prepared by both methods was estimated from their ultraviolet circular dichronic spectra and are similar. We are now preparing several large peptides from the toxin molecule. Digestion of toxin, cell extract or culture filtrate preparations, with papain followed by gel filtration, allows the separation of at least one large atoxic peptide, one large toxic peptide and a fraction containing very small peptides. We have now separated filtrate toxin by gel electrophoresis and gel filtration in the presence of appropriate reducing agents, into two large peptides. These large peptides will now be treated with cyanogen bromide which should produce about 8 peptides and 5 peptides from the heavy and light chains respectively. Fragmentation with trypsin should yield an appreciably larger number of peptides. Peptide from each fragmentation procedure will be separated and sequenced. If a peptide is too large for overlap other enzymes will be used. The amino acid composition of peptides, prepared by cyanogen bromide and trypsin cleavage from both cell extract and culture filtrate toxin will be compared. This should detect any difference in the two toxins. There is no apparent reason to sequence toxin prepared by both methods. These experiments should allow us to compare the amino acid sequence of this unusual protein with its secondary structure and that of other nontoxic soluble proteins. It should also enhance our understanding of the molecular mechanism of the pathology of tetanus and ultimately aid in the prevention and care of this deadly disease.